Magnetic forming apparatus



Feb. 18, 1969 JANSEN MAGNETIC FORMING APPARATUS Filed Nov. 7, 195

. I N VEN'I'OR. fihlva/oea AAA/517V 1 I i 6F AT'mRmms United States Patent 3,427,842 MAGNETIC FORMING APPARATUS Hansjorg Jansen, Santiago, Chile, assignor, by mesne assignments, to Gulf General Atomic Incorporated, San

Diego, Calif., a corporation of Delaware Filed Nov. 7, 1966, Ser. No. 592,378

U.S. Cl. 72-56 Int. Cl. B21d 26/02, 26/14; B21j /04 Claims ABSTRACT OF THE DISCLOSURE This invention relates to forming apparatus and, more particularly, to apparatus for forming material by energy acquired from a varying magnetic field.

Apparatus has been developed for forming materials by employing varying magnetic fields of high intensity. An example of such apparatus is shown and described in the United States Patent No. 2,976,907, issued Mar. 28, 1961, and assigned to the assignee of the present invention. In apparatus of this general type, an electrical current pulse of high amperage is passed through a forming element comprising a conductor ('e.'g., in the form of a coil) to provide a desired magnetic field of high intensity. The current pulse may vbe applied to the conductor directly from a current pulse source or may be induced in the conductor by suitable inductive elements positioned adjacent thereto. A conductive work piece positioned in the pulsed magnetic field produced by the conductor has a current pulse induced in it. This current pulse interacts with the pulsed magnetic field to produce a force acting on the work piece. If the force is sufficiently strong, a deformation of the work piece results. The shape of the deformation is dependent upon the distribution in time and space of the magnetic field and the position of the work piece relative to the field. Repeated pulses of current may be applied to or induced in the conductor, thus causing a series of deforming impulses to act upon the work piece.

In deforming a relatively short portion of a Work piece, for example, in producing an annular constriction or bulge intermediate the ends of a tube, proper concentration of the force of the magnetic field may be achieved by making the conductor in a single turn or loop. To apply the current pulse the single loop conductor needs terminals which in turn cause an interruption of the otherwise closed loop. A radial gap is provided at one point of the periphery of the conductor. To reduce the effects of this gap on the distribution of the field at the work piece, the gap is made as narrow as possible while still maintaining adequate insulation between the two opposed surfaces of the gap. Even with a narrow gap, there is a lessening of field strength in the region of the gap and a corresponding reduction in the force acting upon the work piece at this region. This nonuniform application of pressure around the work piece results in uneven forming thereof.

It is an object of this invention to provide an improved single turn forming element for use in magnetic forming apparatus, which element is provided with means for increasing the field strength at the gap.

Another object of the invention is to provide a forming 3,427,842 Patented Feb. 18, 1969 element for use in magnetic forming apparatus, which element effects a uniform application of pressure about the periphery of a work piece.

Other objects and the various advantages of the invention will become apparent to those skilled in the art from the following description taken in connection with the accompanying drawing wherein:

FIGURE 1 is a plan view of a forming element for use in magnetic forming apparatus, which element is constructed in accordance with the invention;

FIGURE 2 is an elevational View of the forming element of FIGURE 1;

FIGURE 3 is an enlarged sectional view taken along the line 33 of FIGURE 1;

FIGURE 4 is a schematic perspective view of a portion of a forming element which is not constructed in accordance with the invention and which is shown for purposes of comparison; and

FIGURE 5 is a schematic perspective view of a portion of a forming element constructed in accordance with the invention.

The forming element of the invention is for use in magnetic forming apparatus and, in the preferred embodi- .ment shown, comprises a conductor 11 having a first surface 12 defining a generally annular path. The term generally annular path, as used herein, is intended to include noncircuiar, as well as circular, paths in the nature of a single loop or turn. The conductor has at least one gap 13 therein extending from the first surface. The conductor is responsive to pulses of electrical energy applied thereto to conduct a current for producing a magnetic field adjacent the surface 12 for deforming a work piece (not shown) disposed in the magnetic field. The conductor has a pair of recesses 14 and 16 therein on opposite sides of the gap. Each of the recesses extends from a surface 17 of the conductor opposite the first surface 12 toward the associated corner of the gap 13 across a substantial portion of the distance therebetween. Current flowing through the conductor is thereby concentrated at the corners of the gap to maintain the strength of the deforming magnetic field at the gap 13.

Referring now in more detail to the preferred form of the apparatus shown in the drawings, the particular type of forming element therein illustrated is an expansion type element. An expansion type element is utilized for deforming the walls of a hollow work piece radially outward from the forming element. A die may surround the outer surface of the work piece to effect a particular detail in the deformed portion of the work piece. It is to be understood, however, that the invention is of equal applicability to forming elements of the compression type. The latter type of forming elements surround the outer surface of a work piece and serve to deform the work piece radially inward. An example of how the illustrated device may be modified to constitute a compression type forming element rather than an expansion type element will be described subsequently.

In the illustrated embodiment, the conductor 11 is annular in configuration and includes a first segment 18 comprising the greater portion of the conductor and further includes a second segment 19 secured to the first segment and completing the annular conductor. The second segment is preferably secured to the first segment by brazing or other processes of metal joining at the mating surfaces. Segments 18 and 19 could also be machined from one single piece of metal, to avoid fatigue problems which might be introduced by the joining process.

The second segment 19 is in two separate halves with the gap 13 acting to separate the two halves of the second segment. Suitable insulation (not shown) is disposed in the gap. The two halves of the second segment 19 extend inwardly of the annular conductor 11 toward the center thereof. A pair of extensions 21 and 22 project from the second segment 19 and are, respectively, secured to the two halves of the second segment. Again, the extensions 21 and 22 and the segment 19 may be machined from one piece of metal. The extensions 21 and 22 project generally parallel with the axis of the annular conductor 11 and the gap 13 is continued between the extensions 21 and 22. The extensions 21 and 22 are provided with flanges 23 and 24, respectively, at the opposite ends of the extensions from the second segment 19. The flanges extend normally from the extensions in opposite directions. The flanges 23 and 24 include a plurality of holes 26 therein by which the flanges may be attached to a suitable supporting member, not shown, by bolts or screws. The supporting member may include a pair of suitable electrical conductors for electrically connecting the two halves of the second segment 19, through the extensions 21 and 22, across a source of pulsed current, not shown. In the case of an expansion type forming element, as illustrated, the supporting member may be elongated to facilitate the insertion of the forming element into the hollow interior of a work piece.

If it is desired that the forming element be of the compression type rather than the expansion type shown, the two halves of the second segment may extend outwardly of the annular conductor 11, rather than inwardly as shown. The extensions 21 and 22 and their corresponding flanges 23 and 24 will thereby lie outside of the annular conductor to permit the insertion of a work piece into the opening defined by the annular conductor. By such a modification, the magnetic field produced by current flowing around the inner surface of the annular conductor will exert a force on the work piece directed radially inward to compress the work piece, rather than radially outward to expand the work piece as would be the case with the illustrated device. The invention is of equal applicability to both expansion and compression type devices.

Since considerable heat may be produced in the conductor 11 due to the high currents flowing therein, a suitable passage for coolant flow may be provided in the conductor. In the illustrated embodiment, the first segment 18 of the conductor 11 is comprised of a first portion 27 of substantially Ushaped cross section. A second portion 28 is secured to the first portion 27 (preferably by brazing) over the open side of the portion 27 to define a coolant passage 29. A pair of fluid conduits 31 and 32 are attached to the conductor 11 and communicate with the fluid passage 29 through suitable openings 33 and 34, respectively, in the first portion 27 of the conductor. The conduits 31 and 32 are disposed on opposite sides of the second segment 19 of the conductor 11 proximate thereto. The second segment 19 is not provided with a coolant passage and thereby acts to block the coolant passage 29. Accordingly, a fluid flow through the passage 29 may be established by conducting fluid to the passage through one of the conduits 31 and 32 and removing fiuid from the passage through the other of the conduits. The flow of coolant through the passage will thereby remove heat from the conductor 11 such that it operates at relatively cool temperature levels.

The distribution of the magnetic field produced by the conductor 11 is made more uniform by providing, as shown in FIGURE 1, the pair of recesses 14 and 16 on opposite sides of the gap 13. These recesses extend from the inner surface 17 of the conductor 11, and extend across a substantial portion of the distance between the inner surface 17 and outer surface 12, preferably more than half way. The recesses also preferably extend diagonally from the surface 17 toward the corner of the gap at the outer surface 12.

The reduced portions of the conductor 11 produced at the gap corners by these recesses 14 and 16 cause the pulsed current passing through the conductor to be concentrated at the corners. Without these reduced portions,

there is a tendency for the current to spread out more at the corners of the gap than at the remaining circumference of the conductor. This is illustrated in the schematic drawing of FIGURE 4 wherein the lines on the surfaces of the portion of the conductor illustrated therein represent the current flow in the surface layers of the conductor. Since the current is pulsed, the current flows in the surface layers as is normally the case with high frequency current. The forming element of FIGURE 4 is not constructed in accordance with the invention, however, portions thereof corresponding to portions of the element of FIGURES 1-3 are indicated by identical reference numbers followed by the letter a. As a result of the increased perimeter of the cross section of the corner as compared to the perimeter of the cross section of the rest of the conductor 11, there is a tendency for the current to spread. Hence, the current density on the surface 12 at the gap corner is reduced, which correspondingly reduces the strength of the magnetic field in the region of the gap. This means that less force will be exerted on the work piece in the region of the gap than in the other regions of the magnetic field, causing a nonuniform peripheral pressure and consequent uneven forming of the work piece.

Referring particularly to FIGURE 5, the result of adding the recesses 14 and 16 is illustrated schematically. The current is represented by the lines on the surfaces of conductor 11. It will be seen that when the recesses 14 and 16 are provided, the effective surface area near the gap 13 is reduced. Thus, current on the surfaces of the conductor 11 is concentrated at the gap corner. By proper selection of the size and position of the recesses, the result obtained is that the magnetic field in the region of the gap 13 is not diminished and therefore a more uniform forming pressure is exerted on the work piece.

A satisfactory device has been constructed wherein the distance between the surfaces 17 and 12 was 0.295 inch, wherein each recess was inch wide with a /32 inch radius at the inner end thereof, wherein the center of such radius was 0.12 inch from both the surface 12 and the closest surface defining the gap 13, and wherein the angle between each recess and the closest surface defining the gap 13 was about 16.

The forming elements thus far described herein are such as have the current pulse applied directly thereto. Another type of forming element, known as a field shaper, is sometimes utilized in magnetic forming apparatus. Such an element is generally in the form of a conductive body having at least one opening therein for receiving a work piece. The field shaper is disposed relative to an inductive element or elements, such as an induction coil, so that a current pulse applied to the inductive element or elements will induce a current pulse in the field shaper. This current is concentrated on the surface of the conductive body around the opening therein, and produces a magnetic field in the opening for forming the work piece. A radial gap is provided in the conductive body of the field shaper so that the shaper does not act as a shorted turn. Thus, the conductive body of the field shaper constitutes a single loop conductor (i.e., the inner surface layer and the outer surface layer connected together by the gap surface layers). The problem of current spreading at the gap is present here also, and may be solved by providing suitable recesses in the conductive body so as to concentrate current at the gap corners adjacent the surface around the opening.

It will therefore be seen that the invention provides an improved forming element for use in magnetic forming apparatus. In a preferred form, the forming element comprises a single loop conductor constructed in a way that insures production of a uniform magnetic field. Various modifications and embodiments of the invention, other than those shown and described herein, will be apparent to those skilled in the art from the foregoing description. Such modifications and embodiments are also intended to fall within the scope of the appendant claims.

What is claimed is:

1. A forming element for use in magnetic forming apparatus, comprising, a conductor responsive to pulses of electrical energy applied thereto to conduct a current for producing a magnetic field for forming a work piece disposed in the magnetic field, said conductor having a first surface of finite length defining a current path for producing the magnetic field and having a second surface contiguous with said first surface at one end thereof for conducting current to or from said first surface, said conductor further having a third surface opposite said first surface, said conductor having a recess therein proximate said second surface, said recess extending from said third surface of said conductor toward said first surface across a substantial portion of the distance between said first and third surfaces to concentrate current flowing on said conductor toward said first surface of said conductor, whereby the strength of the forming magnetic field is substantially undiminished near and at the corner between said first and said second surfaces.

2. A forming element according to claim 1 wherein said first surface of said conductor is of generally annular configuration.

3. A forming element according to claim 1 wherein said recess comprises a slot which extends obliquely to said second surf-ace toward the juncture of said first and second surfaces.

4. A forming element for use in magnetic forming apparatus, comprising, a conductor responsive to pulses of electrical energy applied thereto to conduct a current for producing a magnetic field for forming a Work piece disposed in the magnetic field, said conductor having a first surface defining a generally annular current path and having at least one gap therein extending from said first surface, said conductor having a pair of recesses therein on opposite sides of said gap, each of said recesses extending from a surface of said conductor opposite said first surface toward said first surface across a substantial portion of the distance between such surfaces to concentrate current flowing on said conductor toward said first surface of said conductor, whereby the strength of the forming magnetic field is substantially undiminished at said gap.

5. A forming element according to claim 4 wherein said recesses comprise a pair of slots extending from a surface of said con-ductor opposite said first surface toward the corner of said gap at said first surface toward the corner of said gap at said first surface across at least one half the distance between said first and second surfaces.

6. A forming element according to claim 5 wherein said slots extend diagonally toward said corner and wherein the angle between said slots and the closest surface of said gap is of the order of 16.

7. A forming element according to claim 4 wherein said conductor is of annular configuration and includes a finst segment comprising the greater portion of said conductor and a second segment secured to said first segment and completing said annular conductor, said second segment having said gap therein and having a pair of extensions adapted for supporting said conductor.

8. A forming element according to claim 7 wherein said extensions are further adapted for electrical connection to a source of pulsed current.

9. A forming element according to claim 7 wherein said first segment is provided with a coolant passage therein.

10. A forming element according to claim 9 wherein said first segment is comprised of a first portion of substantially U-shaped cross section and a second portion secured to said first portion over the open side thereof to define said coolant passage, and wherein means are provided in one of said first and second portions of said first segment for passing coolant therethrough into and from said coolant passage.

References Cited UNITED STATES PATENTS RICHARD J. HERBST, Primary Examiner. 

